The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A variety of eddy current probes have been developed for inspecting nuclear power plant steam generator tubes over the last few decades. Commercial probes such as bobbin coil probes (absolute and differential modes), rotating probes (Rotating Pancake Coil and Plus-Point), and array probes (X-Probe, Smart Array Probe and Intelligent Probe) have been used extensively in industry.
While these probes are commonplace, they are limited in operation. Conventional bobbin coil probes, while robust and useful for fast initial detection of possible degradation, are not suitable for detecting circumferential defects around the tube. One of the limitations of bobbin coils is that the eddy currents they induce are parallel to the crack orientation. Rotating probes provide a C-Scan image of the tube wall with high resolution, offering superior ability to characterize and size defects. These probes are also sensitive to circumferential defects. Moreover, they use a helical, mechanical scan process that is time-consuming and prone to additional probe wear. Further still, the complexity associated with the mechanical system for rotating the probe can contribute to poor reliability. Array probes are another conventional probe type. These probes are capable of providing information relating to the angular location of defects. The advantages associated with the use of these probes include high inspection speed and resolution. But array probes rely on sophisticated excitation and post-processing schemes. The signal from these probes is commonly contaminated by noise induced by probe vibration.
There is a need for an eddy current probe able to overcome the foregoing deficiencies and provide accurate defect detection over an entire circumference of a vessel with high inspection speed and resolution.